The crash occurred in Chatsworth, about 40km from downtown Los Angeles, near where emergency officials were responding to a deadly bus collision in the area.
Four patients were assessed at the scene, with three pronounced dead and one transported to a local hospital in an unknown condition, according to Los Angeles Fire Department.
The incident caused a fire as the helicopter landed near several vehicles and two large cargo containers, LAFD said.
It was not immediately clear whether some of the people killed in the crash had been in the helicopter.
At least one person killed was outside in the parking lot, Captain Branden Silverman, a spokesperson for the LAFD, told a news conference.
"We're trying to determine how many patients were inside the helicopter," he said.
Capt Silverman described the helicopter as "pretty well destroyed".
According to several media reports, the helicopter involved in the crash was a television news helicopter, as several were in the area reporting on the bus collision.
Reuters could not immediately verify whether the helicopter involved was a TV news helicopter. The LAFD did not immediately respond to requests for further details.
Los Angeles Mayor Karen Bass said she was "devastated" by the loss of life in the helicopter crash and the bus collision in Chatsworth, thanking emergency responders for their swift response.
The National Transportation Safety Board (NTSB) will lead an investigation into the incident.
with Reuters
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